Transition planning server upgrade from 32-bit to 64-bit

I am in the data collection phase for a project proposal to upgrade our citrix presentation server from Windows 2003 32-bit to 64-bit. I was wondering if anyone could point me to a resource for transition planning for this kind of work. I have been looking at the option of using Xen virtual server for hosting the current server whilst working on the new server, but I would really like not to re-invent the wheel, but so far my searches for information on this have been lacking. Thanks in advance.

-Tim